In view of the flow features, a threedimensional wind field model of airflow over mountain in consideration of the ground friction and the leeward vortex are established based on the theory of potential flow. Taking a certain empennage rocket of 122 mm as an example combined with 6DOF ballistic model, this kind of empennagerocket is studied on its ballistic performance of prior trajectory influenced by the airflow over mountain wind shear. The results show that the airflow over mountain wind shear has a certain impact on the flight time, the range, the side-slip, the falling velocity and the angular motion of a rocket, particularly on the lateral movements of a rocket. The wind field strength is positively related to the influences on a rocket by the airflow over mountain; The changing regularity of ballistic performance when the rocket launched on the windward slope is opposite to that of leeward slope and the ballistic performance is more affected when a rocket is launched on the leeward slope. Within the range of middlelow elevation, the incremental elevation of a rocket is enabled to influence on the range of a rocket by the airflow over mountain, meanwhile the influence on the sideslip may increase correspondingly.